Detection devices for use in solution processing systems

ABSTRACT

A detection device for use in a cyclical solution processing system, such as a water softening system, where an ion-exchange material the dimensions of which vary as a function of the salt concentration of and the valence of ions present in the solution is placed on a flexible, solid substrate material of fixed dimensions. The device is placed in contact with the processed solution at or near the system output so that the dimensional changes of the ion-exchange material causes a flexing of the substrate material, which device is then effectively used as a switch in control circuitry for controlling the operating time of one or more of the sub-cycles of operation required in the overall processing cycle.

United States Patent Calmon Dec. 23, 1975 DETECTION DEVICES FOR USE INSOLUTION PROCESSING SYSTEMS [75] Inventor: Calvin Calmon, Birmingham,NJ.

[73] Assignee: Water Purification Associates,

Cambridge, Mass.

[22] Filed: Dec. 19, 1974 [21] Appl. No.: 534,466

[52] US. Cl 210/96; 210/139 [51] Int. Cl. B01D 15/06 [58] Field ofSearch 210/96, 139, 149

[56] References Cited UNITED STATES PATENTS 3,282,650 11/1966 Bannigan23/253 3,477,576 ll/l969 Luck et al 210/96 3,512,643 5/1970 Forss 210/963,578,164 5/1971 Weiss et al. 210/96 3,687,290 8/1972 Myers 210/149Primary Examiner.lohn Adee Attorney, Agent, or Firm-Robert F. OConnell[57] ABSTRACT A detection device for use in a cyclical solutionprocessing system, such as a water softening system, where anion-exchange material the dimensions of which vary as a function of thesalt concentration of and the valence of ions present in the solution isplaced on a flexible, solid substrate material of fixed dimensions. Thedevice is placed in contact with the processed solution at or near thesystem output so that the dimensional changes of the ion-exchangematerial causes a flexing of the substrate material, which device isthen effectively used as a switch in control circuitry for controllingthe operating time of one or more of the sub-cycles of operationrequired in the overall processing cycle.

13 Claims, 8 Drawing Figures U.S, Patent Dec.23, 1975 Sheet10f43,928,200

HAIL

so FTENING AFTER BREAKIHROUGH AT "All B BACKWASH (TIMED) H REGENERATION(TIMED) LEAKAGE SALT LOADING (LBS/F133) 4- LOW HIGH U.S. Patent Dec. 23,1975 Sheet 2 of4 3,928,200

CONSCEIPIFTRATED 32 UNTREATED 23 WATER SOLUTION I SOURCE (REGENERANT)VALVE VALVE 24 To '4-VALVE DUMP 5| 2| To VALVE/TIMER VALVES ACTUATION24, 25 CIRCUITRY 2O 28 3o 52. 26

ION

DETECTOR EXCHANGE TANK 2? TIMER 22 28 I I VALVE w TO VALVES 2 528 30 32VALVE 25 To TREATED wATER 4 DUMP OUTPUT US. Patent Dec.23,1975 Sheet30f43,928,200

' FIGZ) U.S. Patent Dec.23, 1975 Sheet4of4 3,928,200

- RINSE BACKWASH REGENERATION "'-SOFTENING (DEPLETION) Z 9 i- 2 1 2 3 a3 z 53 O A U ZBREAKTHROUGH s I TIME-F'- Z 9 2 2 E 2 LLI 3 g 52 f 8 L m'V TIME DETECTION DEvIcEs FOR USE IN SOLUTION PROCESSING SYSTEMSINTRODUCTION This invention relates generally to devices for detectingcertain points in the operating cycle of a water treatment system andmore particularly, to a device for detecting the end of the service, orprocessing, subcycle and/or the end of the rinse sub-cycle of a watertreatment operating cycle.

BACKGROUND OF THE INVENTION In many sections of the world, water whichis available for use contains'metallic ions such as calcium, magnesium,iron or other ions which make the water too hard for effective usethereof. In order to soften such water (i.e. remove the undesired ionsthereof) ion exchange systems have been utilized wherein the multivalentmetallic ions are exchanged for relatively innocuous mono-valent ionssuch as sodium.

The normal overall operating cycle of such a system usually includes thefollowing four sub-cycles thereof:

1. the Softening sub-cycle wherein the multi-valent ions of the water tobe treated are exchanged for the monovalent ions by the passge of thewater to be treated through a fixed bed of ion exchange material in thesodium form;

2. the Backwash sub-cycle wherein the fixed ion exchange bed iscounter-washed to remove dirt or other undesired solid particles whichmay have become caught in the interstices between the ion exchange resinparticles or beads;

3. the Regeneration sub-cycle wherein the ion exchange material whichhas become effectively depleted of its ions for effective exchangepurposes during the softening sub-cycle is placed in its original sodiumcondition by the use of a regenerant solution which is passed throughthe fixed bed to resupply the monovalent ions as desired in aregenerating ion exchange process; and

4. the Rinse syb-cycle wherein the regenerated ion exchange material isrinsed free of residual salt which has been used in the regenerantsolution and the exchanged ions from the resin.

During such operation, it is desirable to provide the most efficientsystem so that the end of the softening sub-cycle be detected withaccuracy. Such point in the overall operating cycle is often called thebreakthrough point, that is, the point in a water softening process atwhich the softened output water begins to become hard again due to thepresence of the multivalent metallic ions which can no longer be removedtotally once most of the available groups have been utilized. If suchpoint is not accurately detected so that the output water obtained bythe softening process can be appropriately shut off and regeneration ofthe ion exchange material can take place, the undesired metallic ionswill be present in the output water which is to be used and theirpresence will lead to scaling, excessive soap consumption, staining andfouling, etc.

It is also desirable to be able to detect accurately the end of therinse sub-cycle because, if such end point is not known, the outputwater at the start of the softening sub-cycle may have an excessivelyhigh sodium content which condition is undesirable for reasons of bothhealth and taste.

DESCRIPTION OF THE PRIOR ART In many presently known water softeningprocesses which utilize ion exchange materials, the operating cycle isusually determined by timing devices which bring each portion of theoverall cycle to an end after a predetermined time period which can beset, for example, by an operator. Other systems detect breakthrough forexample, by providing devices for monitoring the volume of water whichis being treated, the service sub-cycle shutting off after a specifiedvolume has passed through the monitoring device. Such methods may beinefficient or ineffective if the timing or volume is inaccurate. Forexample, a waste of ion exchange capacity can result if the softeningsub-cyle is shut off too soon or untreated or partially treated waterwill be produced if the softening sub-cycle continues beyond thecapacity of the exchanger. If the sub-cycles are not specifically timed,variations in the volume of water used either in home or in plantoperation can cause the system to operate at less than its optimumeffectiveness. Moreover, if volume is used as a monitoringcharacteristic, a change in the incoming water com position to betreated will also cause a volume measurement system to operate at lessthan its optimum effectiveness.

One device for controlling the operation of the softening sub-cycle hasbeen suggested in US. Pat. No. 3,250,392 issued to J. R. Luck on May 10,1966. The device therein utilizes a ribbon type sensor, the length ofwhich changes depending on the type of ion content of the water to whichit is exposed. The ribbon is in the form of a thin ion exchange membranewhich is mounted so as to be exposed to the water flow. When the wateris soft (i.e. treated water containing sodium only) the ribbon is at itsmaximum length and when the water contains hardness-causing ions (i.e.Ca or Mg), the ribbon shrinks by a pre-determined amount depending onthe content of multi-valued ions exchanged on it. The ribbon isconnected to a switch which opens, or closes, a circuit at the end ofthe softening sub-cycle (at the breakthrough point) so as to control thetime at which energization of the regeneration means occurs.

One of the problems arising from the use of such a thin membrane, orribbon, structure as in the Luck patent, is that the degree ofdimensional sensitivity depends on the cross-linking of the ion exchangematerial used therein. Thus, the lower the cross-linking the greater thevolume, or dimensional, change thereof. However, the lower thecross-linking (i.e. the greater the sensitivity), the weaker themembrane structure, such structures thereby being subject to frequentbreakage in use. Accordingly, the reliability thereof and the costinvolved in shutting down the entire system for replacement of a damagedmembrane makes the use of such a ribbon structure less effective than isdesirable. If an attempt is made to strengthen the ribbon by utilizing arigid inert backing to maintain structural and dimensional integrity,the membrane cannot be utilized since the backing will prevent changesin length thereof.

Moreover, the Luck patent does not suggest any means for effectivelydetermining the end of the rinse sub-cycle, but only deals with thequestion of detecting the end of the softening sub-cycle so thatregeneration can be appropriately actuated.

SUMMARY OF THE INVENTION This invention avoids the problem of structuralweakness inherent in the detection device of the Luck patent and offersa more sensitive and reliable means of detecting not only the end of thesoftening sub-cycle, but also if desired the end of the rinse sub-cycleof the overall system. In accordance therewith, the detector utilizes anion exchange material in film, fiber or granular form, such materialbeing placed on one surfce of a relatively rigid but flexible solidmaterial. The crosslinking of the ion exchange materials can be very lowprovided they are selected so as to be insoluble in solution. The activeion exchange materials are applied to the surface of the solid materialin their most expanded form. When the combined detector structure is incontact with a solution containing multi-valent ions (i.e. the solutioncontains hardness), the ion exchange material shrinks so as to cause theoverall structure to deflect, or bend, out of its normal plane, thechange in curvature thereof being an indication of a change in valenceof the ions forming the counter-ion of the ion exchange material. Suchdeflection accurately detects the point at which break-through (i.e. thepresence of multi-valent ions) occurs at the end of the softeningsub-cycle (i.e. at the point where the effective ion-exchange capacityof the ion-exchanger is reduced).

Moreover, the same detector structure can be utilized to determine theend of the rinse sub-cycle. Thus, the ion exchange material is in adeflected condition when in the presence of a solution having a highconcentration of mono-valent salt ions (i.e. sodium ions as would occurduring the rinse sub-cycle) but is in its extended, or non-deflected,position in the presence of a solution of mono-valent ions of lowconcentration as would occur at the end of the rinse sub-cycle.

The specific structure and use of the detection device of the inventionis described in more detail with the help of the attached drawingswherein FIG. 1 shows a simplified diagrammatic representation of theoverall operating cycle of the system;

FIG. 2 shows a diagrammatic representation of an appropriate watersoftening system utilizing a tank containing a fixed bed ion exchangerwhich system uses the detection device of the invention;

FIGS. 3 and 3A show a more detailed diagrammatic representation of oneembodiment of the detection element of the detection device of theinvention;

FIG. 4 shows the configuration of the detector device at various pointsin the overall operating cycle of the systemshown in FIG. 1;

FIGS. 5 and 5A show a more detailed diagrammatic representation ofanother embodiment of the detection element of the detection device ofthe invention; and

FIG. 6 shows a graphical relationship between leakage and salt loadingin the regenerant solution.

FIG. 1 depicts the overall operating cycle of a typical water softeningsystem. As can be seen therein, in the softening portion 10 of thecycle, untreated water containing hardness-causing ions is changed totreated water containing non-hardness-causing ions by ion exchange, theion-exchange material being effectively depleted or exhausted at the endthereof (Point A). Following the softening portion of the cycle, thedirt and other materials which may be present in the bed of ion exchangematerial is cleansed in a backwash, or counter-wash, portion 11 of thecycle which can be arranged to extend for a pre-determined time periodat a given flow rate through suitable timing means. After thebackwashportion of the cycle, the depleted ion exchange material is regenerated(portion 12 of the cycle) with a salt solution of a given strength at aprearranged flow rate so as to regenerate the ion exchange material andto place it in the condition required for the exchange operation in thenext softening sub-cycle. After the timed regeneration sub-cycle, thebed is rinsed free of the excess regenerant salt solution, as well assome of the exchanged hardness-causing ions which still diffuse out ofthe ion exchange particles. At the end of the rinse process (Point B),the ion exchange material is then ready for use in softening theuntreated water.

The detection device of the invention is utilized to determine both theend of the softening portion of the cycle (Point A) and the end of therinse portion thereof (Point B) or to determine each of such pointsindividually.

A diagrammatic representation of a typical apparatus useful for an ionexchange water softening process is shown in FIG. 2 wherein a fixed bedof ion exchange material in the form of ion exchange beads, orparticles, is contained within a tank 20 into one end of which,identified as the input" end 21, a liquid material to be treated, suchas hard water, is introduced, the treated liquid which has passedthrough the ion exchange bed being obtained at the output end 22.

Thus, during the softening portion of the operating cycle of the system,untreated water from a source is introduced into the input end of ionexchange tank 20 through an appropriate valve 24. As the untreated waterinitially moves through the ion exchange bed, the contaminant ions (e.g.Ca ions) therein are exchanged with the counter ions (e.g. Na ions) inthe ion exchanger in a relatively narrow zone near the top of the bed.The exchange zone effectively travels through the tank at a much slowerrate than the input water, thereby leaving depleted exchange resinparticles behind. Accordingly, treated water, in which the hard ionshave been removed, is available at the output end 22 and can be suppliedvia valve 25. The treated water is continuously supplied until theexchange zone reaches close to the bottom of the bed at which time theion exchange material is depleted for complete softening and thebreak-through of hardness causing ions takes place.

A detector 26 of the type described in more detail, for example, withreference to the embodiments of FIGS. 3 and 4 is appropriatelypositioned outside the tank and a sample of the treated water issupplied thereto. For example, an outlet pipe may be used to obtain thesample and the detector is placed in the outlet pipe, so as to come intocontact with the sampled water, as explained more fully below. At theend of the softening portion of the cycle a break-through appears, thatis, the ion exchange material of the bed in tank 20 becomessubstantially depleted. Accordingly, the multi-valent ions in theuntreated water appear in the water sample supplied at the outlet pipe27 of tank 20. Such break-through point is detected by detector 26 whichcauses valve 24 to be actuated so as to divert the supply of furtheruntreated water from the input of ion exchange tank 20 to a valve 28 forpurposes described below.

At the same time, timer 29 is activated and in turn activates valve 28so that the untreated water supplied thereto from source 23 via valve 24is fed to the output end 22 of tank 20. Such untreated water is therebyforced through the ion exchange bed in a reverse direction so as toclean out dirt or other foreign solids, which may be present in the bed.The back-wash water is then appropriately dumped via valve 30 which hasbeen activated by valve activation circuitry 31.

At the end of the back-wash sub-cycle, as determined by the setting oftimer 29, regeneration of the ion exchange bed must begin. Accordingly,valves 24, 28 and 30 are appropriately actuated so as to end thebackwash portion of the cycle. Simultaneously, timer 29 activates avalve 32 so that a concentrated salt solution from a supply 31 thereof(i.e. the regenerant solution) is supplied to the input 21 of ionexchange tank 20. The sodium ions therein are exchanged for themulti-valent ions in the depleted ion exchange bed so as to resupply thelatter with sodium ions and place it in condition for thesofteningportion of the cycle. The waste regenerant leaving ion exchangeis thereupon dumped via valve 25.

At the completion of the regeneration sub-cycle as appropriately timedby timer 29, valve 32 is activated so as to stop the feeding of saltsolution to the tank. At the same time, valve 24 is actuated so as tosupply untreated water once again from source 23 to the input of ionexchange tank 20 at the beginning of the rinse portion of the operatingcycle. During the rinse subcycle, the regenerated ion exchange bed iscleansed of the residual salt and the exchanged hardness ions whichdiffuse out of the ion exchange particles by the rinse which isdischarged from the tank via valve 25. At the end of the rinsesub-cycle, when the salt concentration of the solution of the sample fedto the detector is extremely low, valve is actuated so that untreatedwater from source 23 again is fed to the input 21 of ion exchange tank20 for softening to supply treated water at tank output 22 as discussedabove.

In a typical operation, the service or processing portion of the cycle,i.e. the softening process in a water softening apparatus, for example,is often arranged so as to provide daily regenerations of the ionexchange bed, such duration being effectively controlled by the size ofthe bed and the rate of flow of the water through it. If costs areminimized the service time can be reduced to shorter time periods, e.g.four to eight hours, so that smaller equipment and a smaller volume ofresin is needed. Continuous operation can be obtained by switchingoperation to another column, for example. The back-wash process iscarried out for about 15 to minutes in a typical installation, thereserve flow being at such a rate that the ion exchange bed tends toexpand by 50 to 100 percent of its original volume. The flow rate iscontrolled to be low enough so that resin particles are not carried outof the tank. At the end of the back-wash, the bed settles so asubstantially uniform packing and any channelling formed during thepreceding service portion of the cycle is removed. The regenerationperiod depends on various parameters, but basically it should be slowenough to assure that adequate exchange takes place. Thus, regenerationmay typically take 20 to 60 minutes for a 24 hour service run.

While regeneration is described above as occurring in a downwarddirection, the regenerant solution could alternatively be fed upwardlythrough the bed, such a regeneration process being referred to ascounter-current regeneration.

The rinse sub-cycle can often'be arranged to provide for an initial slowrinse wherein the rinse water is passed slowly through the bed todisplace the residual regenerant solution which may be collected forrecycling, if desirable. The slow rinse is followed by a relatively fastrinse to clear out any remaining residue of regenerant solution untilthe rinse sub-cycle is ended.

In order to detect the points at which the softening and the rinsesub-cycle end, the detector 26 must be made sensitive to the presence ofions of different valences and also to the concentration of salt in thesolution to which it comes into contact.

As can be seen for example in Table I below, an ion exchange materialshows a volume reduction in the presence of a salt solution as afunction of the concentration thereof, the salt in effect acting as adehydrating agent which shrinks the ion exchange material. The degree ofshrinkage depends not only on the concentration of the salt solutionwith which it is in contact but also on the cross-linking of theexchanger. The table specifically shows the percentage of volumereducton of a cation exchanger comprising a sulfonated copolymer ofstyrene cross-linked with a 1 percent divinyl benzene when it is incontact with sodium chloride solutions of varying concentrations.

TABLE I Concentration of Salt Solution Volume Reduction of ExchangerTABLE II Ratio of Volume of Ion Exchanger Valence of Cation (Compared toSodium State) 1 (e.g., Na 1.0 2 (e.g., MgSTa) 0.5 3 (e.g., Cr 0.25 4(e.g., Th 0.10

The detection device of the invention is fabricated to react to theshrinkage in volume in such a way as to indicate both the end of thesoftening portion of the cycle (at which break-through and the presenceof multi-valent ions occurs) and the end of the rinse portion of thecycle at which the concentration of salt solution changes from arelatively high concentration to a relatively low concentration. FIG. 3shows one embodiment of the detector 26 of the invention which includesa substrate 40 which is a relatively rigid, but flexible, strip of solidbacking material fixedly mounted in an outlet pipe 27 (as shown inphantom) of ion exchange tank 20. The outlet pipe can be appropriatelyopened to sample the liquid which is passing through tank 20, so thatthe sampled liquid comes into contact with detector 26. An ion exchangematerial 41 in a film, fiber or granular form is applied to one surfaceof substrate 40. The active ion exchange material 41 is applied to thesubstrate 40 in its most expanded form so that, in the embodiment ofFIG. 3, the substrate 40 is projected at its full length into theflowing path of the liquid shown by arrows 35. When the liquid incontact with the detector has a relatively low concentration of salt andcontains mono-valent ions such as sodium, the ion exchange material andsubstrate remain in their extended position. A contact member 42 isattached to the free, extreme end of substrate 40 at the surfaceopposite to the surface on which the active ion'exchange material isapplied. A second contact 43 is fixedly mounted in pipe 27 adjacent toand in contact with contact 42 when the detector is so extended. Acontact wire 44 is connected to contact 42 and similarly a wire 45 isconnected to contact 43 and appropriately made available externally tothe pipe via suitably fluid-sealed openings therein. Such wires areconnected in the valve actuation circuitry 30 as explained below morefully. When detector 26 is in its fully extended position, the circuitwithin which wires 44 and 45 are connected is completed through contacts42 and 43.

When the character of the solution which comes into contact withdetector 26 changes, i.e. when the monovalent ions contained therein arereplaced by multivalent ions, or when the relatively low concentrationof salt changes to a relatively high concentration of salt, the volumeof the active ion exchange material 41 is reduced and causes adeflection of substrate 41 so that contact 42 is raised from its contactwith contact 43 and the circuit to which wires 44, 45 are connected isappropriately opened as shown in FIG. 3A.

Accordingly, the operation of detector 26 can be utilized to detect theend of the softening portion or the end of the rinse portion of theoperating cycle. In the first case, the solution with which the detectorcomes into contact changes from one having mono-valent to one havingmulti-valent ions and in the second case the solution changes from onehaving a relatively high salt concentration to one having a relativelylow salt concentration. Such operation is shown in FIG. 4.

As shownin FIG. 4, graph (A) depicts a curve as a function of time ofmulti-valent ion concentration in the liquid which comes into contactwith detector 26 (in the case shown for a water softening process, the.

calcium (Ca) concentration is shown) and graph (B) depicts a curve as afunction of time of sodium concentration in such liquid. The state ofthe detector 26 is depicted diagrammatically below the curves (A) and(B) at key points in the overall cycle time.

Thus, at the beginning of the regenerating portion of the cycle, the Caion concentration at the point at which the detector water sample istaken increases rapidly to a maximum level 50 during which time thepresence of sufficient Ca causes detector 26 to be in its open position.At the same time, the concentration of sodium ions is very low.

During regeneration, the highly concentrated sodium solution is fed totank 20 to replenish the sodium ions in the ion exchange bed viaexchange with the calcium ions. Near the end of regeneration the sampleat detector 26 changes in character to one having a low concentration ofcalcium in the solution, while the concen- 8 tration of sodium in thesolution increases rapidly to a high level 51, as shown. Due to thelatter relatively high sodium solution concentration, the detector 26remains open as shown.

During the rinse portion of the overall operating cycle, the sodiumsolution and sodium particles are washed away and the sodiumconcentration of the liquid sample is rapidly reduced by the end of therinse process as shown at 52. Because of the relatively low sodiumsolution concentration, the detector changes to its fully extendedposition so that its contacts are closed as shown.

The softening portion of the cycle then proceeds with a lowconcentration of calcium and sodium in the detected liquid samplesubstantially throughout. During the softening process, depletion of theion exchange bed continues until the break-through point occurs at whichthe presence of calcium (Ca**) ions reaches a level 53 in the detectedsample at which point the detector opens and the softening process isended. The sodium concentration of the sampled solution also is reducedeven further.

At the latter time, the back-wash portion of the cycle begins and,throughout such process, the calcium concentration continues to rise ata relatively slow rate and the sodium concentration remains very low.Following the timed back-wash process, the regeneration process is againbegun, as discussed above.

Accordingly, the detector 26 is used to identify both the end point ofthe softening process at the breakthrough point 53, where the detectorstate changes from a closed to an open condition, and the end point 52of the rinse process, when the detector state changes from an open to aclosed condition.

An alternative embodiment of the detector switch of FIGS. 3 and 3A isshown in FIGS. 5 and 5A. A solid substrate is attached fixedly at oneend for example to the pipe 27 and projects into the flow path of theliquid at the output thereof. An active ion exchange material 61 in theform of a fiber, for example, is attached to substrate 60 at its endpoints 62 and 63 via an appropriate adhesive. When the active ionexchange material 61 is in its fully extended position, a contact 64 atthe center thereof is adjacent to and in contact with a contact 65fixedly positioned substantially at the center of substrate 60 so thatthe circuit to which wires 66 and 67, respectively, are attached, iscompleted. When the ion exchange material is in contact with a liquidsolution having multi-valent ions or having a high salt concentration,the ion exchange material 61 shrinks in volume so that the substrate 60is deflected outwardly from its center and the contact made by contactelements 64 and 65 is opened as shown in FIG. 5A. The detector acts asan appropriate switch in a manner similar to that discussed in referenceto FIG. 3. Since the electrical resistance of the liquid separating thetwo metal contacts when they are in their separated condition in eitherFIGS. 3A or 5A is extremely high, the detection device as shown thereinprovides a very sensitive indication of the dimensional change of theion exchange material. The force needed to deflect the inert backingmaterial is relatively small and, accordingly, the shrinkage requiredfrom the ion exchange material in order to open the electrical contactsis also very small. Such shrinkage is much smaller, for example, thanwould be required if an ion exchange membrane or ribbon is directlyconnected to a micro-switch contact, as described in the aforesaid Luckpatent.

9 Thus, the inventive structure provides a relatively strong andreliable ion exchange detection device available for determining'boththe end of the softening portion and the rinse portion of the overalloperating cycle of a water softening system.

One aspect of ion exchange water processing systems which represents arelatively significant part of the overall costs of operation thereoflies in the cost of the regenerant solutions when such solutions areheavily loaded with salt. In order to reduce such costs, water softeningprocesses have recently tended to limit the dosages of regenerant saltsolutions used therein so that the quantity of salt available forregeneration is reduced considerably. If the salt loading is so reducedin the system of the invention, the amount of salt available at theoutlet pipe 27 near the bottom of the tank for regenerating the sensorcan be insufficient for the sensor to regenerate to its original state.Accordingly, not all of the ions of calcium, magnesium, etc. (Ca**, Mg,etc.), on the sensor are exchanged for the sodium ions in the regenerantsalt solution during the regeneration sub-cycle.

Further, when relatively low dosages of regenerant salt solution areused, traces of hardness-causing ions may be present in the water duringthe softening subcycle. Such leakage" of hardness-causing ions must beheld to acceptable levels and depends upon the density, i.e. theloading, of the salt in the regenerant solution. As graphically shown inFIG. 6, leakage varies as a function of salt loading (expressed, forexample, in lbs./ft. so that at relatively low salt loadings, theleakage is extremely high, such leakage reducing to a minimal level asthe loading is increased. In a specific water processing system, forexample, the minimum salt dosage that can be used will be determined bythe amount of leakage which is acceptable in a particular applicationfor which the process is being used. For example, if an acceptableleakage level is selected as being at Point A a salt loading level, asshown in Point B can be used.

Furthermore, if iron is present in the water being processed, such ironcan be released during the regeneration sub-cycle and, thereupon, aportion thereof may be deposited on the sensor element and, accordingly,foul the sensor and adversely affect its operation.

Hence, if a relatively low loading of salt is used in the regenerantsolution to save costs, some modification in the operation of the sensoris required in order to provide effective operation thereof.

In one such modification, the sensor can be arranged to operateintermittently, i.e. the-sensor operation is controlled so that itsamples the output of the tank at outlet 27 at separate intervals duringcertain portions of the overall processing cycle. As shown in FIG. 4,the 2 sensor element can be arranged so that it is exposed to theeffluent at outlet 27-near the bottom of the tank 20 on an intermittentbasis beginning at a selectable point in time relatively near to the endof the service subcycle as shown for example at point T prior to thebreak-through point at the end of such sub'cycle. During the earlierportion of the service sub-cycle, i.e. from the point at the end of therinse sub-cycle to a point T, the system operation is arranged so thatthe sensor is not exposed to the effluent at all. After break-through isreached at the end of the softening sub-cycle, the sensor is deflected,the amount of such deflection depending upon the hardness of theeffluent. Accordingly, the system can be arranged so that when the 10sensor reaches a certain predetermined deflection position, the effluentis again diverted from the outlet 27 and the sensor is thereby preventedfrom exposure thereto.

At the end of the back-wash sub-cycle, the system is arranged so thatthe regenerant solution is directed to the sensor directly from thesource thereof. Thus, regeneration of the sensor is not dependent on thecharacteristics of regenerant solution which is present at outlet 27.During the regeneration sub-cycle, the sensor is thereby directlyexposed to regenerant solution, and is not exposed to the effluent atoutlet 27.

At the start of the rinse sub-cycle the sensor is still not exposed tothe effluent and remains in such state until a point T near the end ofthe rinse sub-cycle, at which point the sensor has a predetermineddeflection. At T the detector is again exposed to the effluent on anintermittent basis during the rinse sub-cycle.

At the end of the rinse sub-cycle, the system is arranged to divert theeffluent again from the outlet 27 so as to prevent exposure of thedetector thereto from the beginning of the service sub-cycle until theselected point T near the end thereof.

The above operation of the detector, wherein it is only intermittentlyexposed to the effluent at outlet 27 and wherein the regenerant solutionis applied directly to the sensor permits the sensor to becomecompletely regenerated and avoids exposure thereof to hardnesscausingions present because of leakage during the service sub-cycle. Moreover,since the detector is not exposed to the effluent during regeneration,none of the iron released in the regeneration sub-cycle can be depositedon the sensor.

While the detection device of the invention has been described withreference to its use in a water softening process, it can be used inother processes where detection of an ion exchange depletion or a changein salt concentration is required, either in different processes or inthe same overall process.

For example, the detector may be used in metal plating applicationsinvolving the purification of chromic acid plating and anodizing baths.In such applications, an additional step is used wherein the feedsolution is drained down to the top of the resin bed in the tank aftercompletion of the service portion of the cycle and before the back-washprocess is begun. The feed solution in the bed is then slowly displacedwith treated water and the treated water is then treated again in thefollowing cycle. Such a procedure minimizes the amount of chromic acidsent to waste with the rinse water. The detector of the invention mayalso be used in other applications using dual-bed and mixed bedoperations often used in de-ionizing water.

Accordingly, the invention is not to be deemed as limited to thespecific configuration and uses shown herein except as defined by theappended claims.

What is claimed is:

1. A detection device for use in a solution processing system, saiddevice comprising a sensing element including a first ionexchangematerial the dimensions of which vary as a function of the saltconcentration of said solution and as a function of the valence of ionspresent in said solution when said element is in contact with saidsolution, said first material having maximum dimensions when it is incontact with a solution having mono-valent ions whereby said sensingelement is in its unflexed state and having 1 1 reduced dimensions whenit is in contact with a solution having multi-valent ions whereby saidsensing element is in its flexed state and said first material furtherhaving its maximum dimensions when it is in contact with a salt solutionhaving a relatively low salt concentration whereby said sensing elementis in its unflexed state and having reduced dimensions when it is incontact with a salt solution having a relatively high salt concentrationwhereby said sensing element is in its flexed state;

a second, substantially flexible, solid material having substantiallyfixed dimensions which are retained in the presence of said solutionindependently of the salt concentration thereof and the valence of ionstherein;

said first material being in contact with a surface of said flexible,solid material,

whereby dimensional changes of said first material which occur when saidfirst material is in contact with said solution cause a flexing of saidsensing element due to the flexing of said second material.

2. A detection device in accordance with claim 1 for use in a solutionprocessing system having a system input for feeding a solution to beprocessed and a system output for supplying a'processed solution, andfurther including means for positioning said sensing element at alocation such that during the processing of said solution said detectiondevice is in contact with said solution near said system output; and

means responsive to the flexing of said second material for indicating achange in the characteristics of said solution with respect to the saltconcentration thereof and the valence of ions therein.

3. A detection device in accordance with claim 2 wherein said indicatingmeans include first electrical contact means mounted on said sensingelement; second electrical contact means mounted in a fixed spatialrelationship with respect to said first contact means, said first andsecond electrical contact means forming a part of an electrical circuit;

whereby said flexing of said sensing element causes an opening orclosing of said electrical circuit.

4. A detection device in accordance with claim 3 for use in a solutionprocessing system having an overall operating cycle which includes anion-exchange processing sub-cycle, an ion-exchange regeneration subcycleand a rinse sub-cycle.

said sensing element of said detection device changing from its unflexedstate to its flexed state substantially at the end of said ion-exchangeprocessing sub-cycle, remaining in its flexed state during saidion-exchange regeneration sub-cycle and changing from its flexed stateto its unflexed state substantially at the end of said rinse sub-cycle.

5. A detection device in accordance with claim 3 wherein said secondmaterial of said sensing element is formed as a band fixedly mounted atone end thereof and having said first electrical contact means mountedthereon at a position remote from said one end;

said first material is applied to one surface of said second material;and

12 said second electrical contact means is fixedly mounted to be incontact with said first electrical contact means when said sensingelement is in its unflexed state and to be out of contact with saidfirst contact means when said sending element is in its flexed state.

6. A detection device in accordance with claim 3 wherein said secondmaterial of said sensing element is formed as a band fixedly mounted atone end thereof and having said first electrical contact means mountedthereon at a position remote from said one end;

said first material is applied to one surface of said second material;and

said second electrical contact means is fixedly mounted to be out ofcontact with said first contact means when said sensing element is inits unflexed state and to be in contact with said first contact meanswhen said sending element is in its flexed state.

7. A sensing device in accordance with claim 5 wherein said firstelectrical contact means is positioned at the other end of said band ofsaid second material.

8. A sensing device in accordance with claim 6 wherein said firstelectrical contact means is positioned at the other end of said band ofsaid second material.

9. A sensing device in accordance with claim 3 wherein said secondmaterial of said sensing element is fixedly mounted at one end thereofand said first electrical contact means being attached thereto betweenthe ends thereof; and

said first material is fixedly mounted at its ends to said secondmaterial, said second electrical contact means being attached theretobetween the ends thereof so that said first electrical contact means isin contact with said second electrical contact means when said sensingelement is in its unflexed state and is out of contact with said secondelectrical contact means when said sensing element is in its flexedstate.

10. A sensing device in accordance with claim 9 wherein said first andsaid second electrical contact means are each positioned substantiallyat the centers of said second and first materials, respectively, betweenthe ends thereof.

11. A detection device in accordance with claim 4 wherein said detectiondevice is out of contact with the solution at the output of said systemduring a portion of said ion-exchange processing sub-cycle and isintermittently in contact with the solution at the output of said systemduring the remaining portion of said ion-exchange processing sub-cycle.

12. A detection device in accordance with claim 11 and further whereinsaid detection device is out of contact with the solution at the outputof said system during said regeneration sub-cycle and is in directcontact with a regenerant solution during said regeneration sub-cycle.

13. A detection device in accordance with claim 12 and further whereinsaid detection device is out of contact with the solution at the outputof said system during said rinse sub-cycle.

1. A DETECTION DEVICE FOR USE IN A SOLUTION PROCESSING SYSTEM, SAIDDEVICE COMPRISING A SENSING ELEMENT INCLUDING A FIRST ION-EXCHANGMATERIAL THE DIMENSIONS OF WHICH VARY AS A FUNCTION OF THE SALTCONCENTRATION OF SAID SOLUTION AND AS A FUNCTION OF THE VALENCE OF IONSPRESENT IN SAID SOLUTION WHEN SAID ELEMENT IS IN CONTACT WITH SAIDSOLUTION, SAID FIRST MATERIAL HAVING MAXIMUM DIMENSIONS WHEN IT IS INCONTACT WITH A SOLUTION HAVING MONO-VALENT IONS WHEREBY SAID SENSINGELEMENT IS IN ITS UNFLEXED STATE AND HAVING REDUCED DIMENSIONS WITH ITIS IN CONTACT WITH A SOLUTION HAVING MULTI-VALENT IONS WHEREBY SAIDSENSING ELEMENT IS IN ITS FLEXED STATE AND SAID FIRST MATERIAL FURTHERHAVING ITS MAXIMUM DIMENSIONS WHEN IT IS IN CONTACT WITH A SALT SOLUTIONHAVING A RELATIVE LOW SALT CONCENTRATION WHEREBY SAID SENSING ELEMENT ISIN ITS UNFLEXED STATE AND HAVING REDUCED DIMENSIONS WHEN IT IS INCONTACT WITH A SALT SOLUTION HAVING A RELATIVELY HIGH SALT CONCENTRATIONWHEREBY SAID SENSING ELEMENT IS IN ITS FLEXED STATE; A SECOND,SUBSTANTIALLY FLEXIBLE, SOLID MATERIAL HAVING SUBSTANTIALLY FIXEDDIMENSIONS WHICH ARE RETAINED IN THE PRESENCE OF SAID SOLUTIONINDEPENDENTLY OR THE SALT CONCENTRATION THEREOF AND THE VALENCE OF IONSTHEREIN; SAID FIRST MATERIAL BEING IN CONTACT WITH A SURFACE OF SAIDFLOXIBLE, SOLID MATERIAL, WHEREBY DIMENSIONAL CHANGES OF SAID FIRSTMATERIAL WHICH OCCUR WHEN SAID FIRST MATERIAL IS IN CONTACT WITH SAIDSOLUTION CAUSE A FLEXING OF SAID SENSING ELEMENT DUE TO THE FLEXING OFSAID SECOND MATERIAL.
 2. A detection device in accordance with claim 1for use in a solution processing system having a system input forfeeding a solution to be processed and a system output for supplying aprocessed solution, and further including means for positioning saidsensing element at a location such that during the processing of saidsolution said detection device is in contact with said solution nearsaid system output; and means responsive to the flexing of said secondmaterial for indicating a change in the characteristics of said solutionwith respect to the salt concentration thereof and the valence of ionstherein.
 3. A detection device in accordance with claim 2 wherein saidindicating means include first electrical contact means mounted on saidsensing element; second electrical contact means mounted in a fixedspatial relationship with respect to said first contact means, saidfirst and second electrical contact means forming a part of anelectrical circuit; whereby said flexing of said sensing element causesan opening or closing of said electrical circuit.
 4. A detection devicein accordance with claim 3 for use in a solution processing systemhaving an overall operating cycle which includes an ion-exchangeprocessing sub-cycle, an ion-exchange regeneration sub-cycle and a rinsesub-cycle. said sensing element of said detection device changing fromits unflexed state to its flexed state substantially at the end of saidion-exchange processing sub-cycle, remaining in its flexed state duringsaid ion-exchange regeneration sub-cycle and changing from its flexedstate to its unflexed state substantially at the end of said rinsesub-cycle.
 5. A detection device in accordance with claim 3 wherein saidsecond material of said sensing element is formed as a band fixedlymounted at one end thereof and having said first electrical contactmeans mounted thereon at a position remote from said one end; said firstmaterial is applied to one surface of said second material; and saidsecond electrical contact means is fixedly mounted to be in contact withsaid first electrical contact means when said sensing element is in itsunflexed state and to be out of contact with said first contact meanswhen said sending element is in its flexed state.
 6. A detection devicein accordance with claim 3 wherein said second material of said sensingelement is formed as a band fixedly mounted at one end thereof andhaving said first electrical contact means mounted thereon at a positionremote from said one end; said first material is applied to one surfaceof said second material; and said second electrical contact means isfixedly mounted to be out of contact with said first contact means whensaid sensing element is in its unflexed state and to be in contact withsaid first contact means when said sending element is in its flexedstate.
 7. A sensing device in accordance with claim 5 wherein said firstelectrical contact means is positioned at the other end of said band ofsaid second material.
 8. A sensing device in accordance with claim 6wherein said first electrical contact means is positioned at the otherend of said band of said second material.
 9. A sensing device inaccordance with claim 3 wherein said second material of said sensingelement is fixedly mounted at one end thereof and said first electricalcontact means being attached thereto between the ends thereof; and saidfirst material is fixedly mounted at its ends to said second material,said second electrical contact means being attached thereto between theends thereof so that said first electrical contact means is in contactwith said second electrical contact means when said sensing element isin its unflexed state and is out of contact with said second electricalcontact means when said sensing element is in its flexed state.
 10. Asensing device in accordance with claim 9 wherein said first and saidsecond electrical contact means are each positioned substantially at thecenters of said second and first materials, respectively, between theends thereof.
 11. A detection device in accordance with claim 4 whereinsaid detection device is out of contact with the solution at the outputof said system during a portion of said ion-exchange processingsub-cycle and is intermittently in contact with the solution at theoutput of said system during the remaining portion of said ion-exchangeprocessing sub-cycle.
 12. A detection device in accordance with claim 11and further wherein said detection device is out of contact with thesolution at the output of said system during said regeneration sub-cycleand is in direct contact with a regenerant solution during saidregeneration sub-cycle.
 13. A detection device in accordance with claim12 and further wherein said detection device is out of contact with thesolution at the output of said system during said rinse sub-cycle.